Implement biquad filter for audio renderer effects

Originally the biquad filter was disabled due to issues with crackling before.

src/audio_core/command_generator.cpp

@@ -270,11 +270,9 @@ void CommandGenerator::GenerateBiquadFilterCommandForVoice(ServerVoiceInfo& voic
         }
 
         // Generate biquad filter
-        //        GenerateBiquadFilterCommand(mix_buffer_count, biquad_filter,
-        //        dsp_state.biquad_filter_state,
-        //                                    mix_buffer_count + channel, mix_buffer_count +
-        //                                    channel, worker_params.sample_count,
-        //                                    voice_info.GetInParams().node_id);
+        GenerateBiquadFilterCommand(mix_buffer_count, biquad_filter, dsp_state.biquad_filter_state,
+                                    mix_buffer_count + channel, mix_buffer_count + channel,
+                                    worker_params.sample_count, voice_info.GetInParams().node_id);
     }
 }
 
@@ -302,8 +300,9 @@ void AudioCore::CommandGenerator::GenerateBiquadFilterCommand(
 
     for (int i = 0; i < sample_count; ++i) {
         const auto sample = static_cast<s64>(input[i]);
-        const auto f = (sample * n0 + s0 + 0x4000) >> 15;
-        const auto y = std::clamp(f, int32_min, int32_max);
+        const auto f = (sample * n0 + s0 + 0x2000) >> 14;
+        const auto y = static_cast<s64>(std::clamp(f, int32_min, int32_max));
+
         s0 = sample * n1 + y * d0 + s1;
         s1 = sample * n2 + y * d1;
         output[i] = static_cast<s32>(y);
@@ -389,18 +388,33 @@ void CommandGenerator::GenerateI3dl2ReverbEffectCommand(s32 mix_buffer_offset, E
 
 void CommandGenerator::GenerateBiquadFilterEffectCommand(s32 mix_buffer_offset, EffectBase* info,
                                                          bool enabled) {
-    if (!enabled) {
-        return;
-    }
-    const auto& params = dynamic_cast<EffectBiquadFilter*>(info)->GetParams();
+    auto* effect = dynamic_cast<EffectBiquadFilter*>(info);
+    const auto& params = effect->GetParams();
     const auto channel_count = params.channel_count;
-    for (s32 i = 0; i < channel_count; i++) {
-        // TODO(ogniK): Actually implement biquad filter
-        if (params.input[i] != params.output[i]) {
+
+    if (!enabled) {
+        for (s32 i = 0; i < channel_count; i++) {
             const auto* input = GetMixBuffer(mix_buffer_offset + params.input[i]);
             auto* output = GetMixBuffer(mix_buffer_offset + params.output[i]);
             ApplyMix<1>(output, input, 32768, worker_params.sample_count);
         }
+    } else {
+        const BiquadFilterParameter filter_params{
+            .enabled = true,
+            .numerator = params.numerator,
+            .denominator = params.denominator,
+        };
+        auto& states = effect->GetState();
+        const auto need_init = params.status == ParameterStatus::Initialized ||
+                               params.status == ParameterStatus::Updating;
+        for (s32 i = 0; i < channel_count; i++) {
+            if (need_init) {
+                states[i].fill(0);
+            }
+            GenerateBiquadFilterCommand(mix_buffer_offset, filter_params, states[i],
+                                        params.input[i], params.output[i],
+                                        worker_params.sample_count, 0);
+        }
     }
 }
 

src/audio_core/effect_context.cpp

@@ -150,6 +150,14 @@ void EffectBiquadFilter::UpdateForCommandGeneration() {
     GetParams().status = ParameterStatus::Updated;
 }
 
+const EffectBiquadFilter::StateType& EffectBiquadFilter::GetState() const {
+    return state;
+}
+
+EffectBiquadFilter::StateType& EffectBiquadFilter::GetState() {
+    return state;
+}
+
 EffectAuxInfo::EffectAuxInfo() : EffectGeneric::EffectGeneric(EffectType::Aux) {}
 EffectAuxInfo::~EffectAuxInfo() = default;
 

src/audio_core/effect_context.h

@@ -244,11 +244,18 @@ private:
 
 class EffectBiquadFilter : public EffectGeneric<BiquadFilterParams> {
 public:
+    using StateType = std::array<std::array<s64, 2>, AudioCommon::MAX_CHANNEL_COUNT>;
     explicit EffectBiquadFilter();
     ~EffectBiquadFilter();
 
     void Update(EffectInfo::InParams& in_params) override;
     void UpdateForCommandGeneration() override;
+
+    const StateType& GetState() const;
+    StateType& GetState();
+
+private:
+    StateType state{};
 };
 
 class EffectAuxInfo : public EffectGeneric<AuxInfo> {